In the use of grapple tongs, it is desirable that pressure be maintained in the hydraulic circuit controlling the closing of the tongs in order to prevent a load carried by the tongs from falling or slipping.
Grapple tong implements are used to grasp and transport loads. These loads sometimes become loose within the grapple, owing to reorientation of the load or leakage of hydraulic fluid from the grapple tong system.
A typical example is the transportation of several logs from a harvesting site to a loading station. This transportation is generally over uneven ground, the logs are of ununiform configuration, and the work vehicle is generally not constructed to isolate the load from impacts during transportation. Shifting of the logs or leakage of hydraulic grapple fluid can cause the logs to fall from the grapple. The resultantly required reloading of the logs in the grapple represents a waste of labor and time. It is, therefore, desirable to provide means for automatically and controllably maintaining the grapple in forcible engagement with the load during shifting of the load and/or hydraullic fluid leakage.